A large class of laboratory glassware includes a glass vessel component, with one stem of a stopcock fused to the lower surface of the vessel such that the bore of the stopcock is contiguous with the interior of the vessel. Another stem of the stopcock serves as a drain through which some or all of the contents of the vessel may be emptied. Examples of this class of glassware are separatory funnels, addition funnels, burets, and certain reaction flasks that, due to their size or the complexity of connected apparatus, are preferably drained through a stopcock fused to the bottom surface.
The stems of the all-glass funnels, flasks, burets, and columns that are currently in use are vulnerable to being struck against bench tops and other objects and surfaces, both in the laboratory and in glassware washing facilities. The stresses resulting from such impacts usually fracture the glass just below the stopcock, or else chip off the end of the stem, which then becomes more vulnerable to further chipping. When the fracture is close to the stopcock, repair is impossible without replacing the stopcock, and it is usually more economical to discard the entire apparatus and purchase a replacement. Manufacturers of laboratory glassware have recognized this problem, and have made frequent attempts to find a solution.
Separatory funnels and burets are being marketed which are breakage-resistant by virtue of being entirely constructed of plastic. Although useful in a teaching laboratory where durability is a prime consideration, they have not been well-accepted by professional chemists, since they are not as transparent as glass, they are not as hard and thus are more easily scratched, and they are less resistant to chemicals.
Other attempts to solve the problem have involved the incorporation of plastic components into glass apparatus, and methods of attaching plastic components to glass apparatus are well-known in the art. The simplest type are friction-fitted connections, where mating plastic and glass parts are simply pressed together. One example involving an elastomeric grommet, which fits into an opening in a glass flask, and into which a plastic tube is inserted, is described in U.S. Pat. No. 3,268,300. Another more elaborate example is provided in U.S. Pat. No. 3,632,119, wherein a plastic fitting is inserted into a glass tube and held in place with polytetrafluoroethylene (PTFE)-clad compressed O-ring seals. The teachings of these two patents are incorporated herein by reference.
There have been burets and separatory funnels commercially available having friction-fitted removable stopcocks. For example, the 2116 buret series marketed by Corning Glass Inc., or the 17021 and 17121 buret and 29050 and 29053 funnel series marketed by Kimble Glass, Inc., incorporate a stopcock assembly, constructed of PTFE, friction-fitted between an upper glass vessel and a lower glass stem. In the case of the Kimble 17121 buret and 29053 funnel, the PTFE stopcock assembly is further attached to the glass vessel via a threaded nut.
Another method of attaching plastic components to glassware is through spirally threaded connections. Threaded glassware and associated plastic parts with mating threads are well-known in the art, and are available on many types of laboratory apparatus. For an example of glass fittings with female threads, and mating plastic connectors with male threads, see U.S. Pat. No. 3,695,642, the teachings of which are hereby incorporated by reference. The more common situation involves glass with male threads, as in a glass vial or bottle with a mating plastic cap. An example of the latter design applied to laboratory glassware is a plastic stem threaded to a glass filtration funnel, such as that sold by Safe-Lab, Inc., of Santee, Calif. under the SAFE-FRIT trademark. These filtration funnels incorporate a polypropylene stem, which is widened at the upper end and attached to the threaded lower portion of a cylindrical glass fritted funnel. The threaded portion of the polypropylene stem is as wide as the funnel itself, thus each size of funnel has a matching size plastic stem. These fritted funnels are used exclusively for filtration and do not incorporate stopcocks.
There exists a need, therefore, for articles of stopcock-equipped glassware that retain the advantages of glass, such as transparency, hardness, and chemical resistance, for both the vessel and the stopcock, without the disadvantage of fragility in the vulnerable stopcock stem. None of the presently available articles fulfill this need. All-plastic articles are less transparent than glass and are easily scratched, while articles with plastic stopcock bodies are opaque just where transparency is especially valuable.